Jashore University of Science and Technology (JUST)
Department of Genetic Engineering and Biotechnology
Assignment: Reproductive Organs and its Function of Cattle.
Submitted By
Submitted To
Md. Riaz Uddin
Prof. Dr. Md. Nazmul Hasan
ROLL: 190633
Professore
Dept. of Genetic Engineering and
Biotechnology
Course Title: Human and Animal
Physiology
Course Code: GEBT 2107
Jashore University of Science and
Technology
Submission Date: 14-05-2022
The Cow’s Reproductive Organs and Its Functions.
The ability of a cow or heifer to successfully mate, conceive, give birth, and raise a healthy calf each year
is essential for profitable and sustainable beef production. A good understanding of anatomy and
physiology of both the male and female is helpful in successfully managing reproduction.
Causes for failures in reproduction must be identified and overcome. Research has led to the development
of numerous techniques for managing the reproductive processes of animals. These techniques provide
many options to help progressive cattle producers accomplish their production goals.
Figure 1. Diagrammatic sketch of the reproductive tract of the cow.
Anatomy
Ultimately, reproductive processes are regulated at the level of the brain. The hypothalamus controls
several body processes and behaviors along with reproductive processes. Body temperature, concentration
and components of body fluids, and the drive to eat and drink are just a few functions of the
hypothalamus. It is classified as a neuroendocrine gland since it sends and receives neural signals through
the nervous system and hormonal messages through the endocrine system.
The second organ, the pituitary gland, sits at the base of the brain. The pituitary is about half an inch in
diameter and weighs about 1 gram. Physiologically, the pituitary is divided into two distinct regions: the
anterior and posterior pituitaries. Each region secretes various hormones that direct body processes. Some
of these hormones are responsible for reproductive events, while others control growth, metabolism, and
water balance.
The female reproductive organs consist of the ovary, uterus, cervix, vagina, and vulva. A sketch of the
reproductive tract of the cow is shown in Figure 1. Female reproductive tracts of various livestock species
are similar to the tract of the cow but differ primarily in the shape of the uterus and cervix.
The oviduct, also known as the Fallopian tube, begins as a funnel-shaped tube that engulfs the ovary.
This funnel portion of the oviduct is called the infundibulum. When ovulation occurs, the oocyte is picked
up by the infundibulum and channeled into the oviduct. Fertilization takes place in the oviduct if viable
sperm are present, but the oocyte remains capable of fertilization for only a short time. Therefore, it is
essential that sperm be present in the oviduct near the time of ovulation. The oocyte moves through the
oviduct into the uterine horn within the next 3 to 4 days. If the ovum is fertilized, it begins embryological
development; if not, it simply degenerates.
The body of the uterus of the cow is short, while the uterine horns are relatively long and well
developed. The fertilized embryo moves from the oviduct into the uterine horn, where fetal and maternal
membrane development begins. This newly developing fetus grows within a layer of membranes called
the placenta, through which nourishment from the dam diffuses. This point of interface is called the
placentome. It is made of the joining of the caruncle (maternal) and cotyledon (fetal). There is no direct
blood connection between the fetus and the dam in the bovine placenta, but rather a complex system that
selectively allows certain molecules to pass from the maternal side of the placenta to the fetal side and
vice versa. It also provides nutrients and carries waste products from the fetus.
The cervix is a denser structure that contains more connective tissue. The bovine cervix is often described
as having a “turkey neck” feel when palpated. It has thick walls and a small opening, or cervical os. The
cervix softens and relaxes around the time of estrus, the period of sexual receptivity. Cervical softening
allows a passageway for sperm at mating and also for expulsion of the fetus at the time of birth. During
pregnancy, the cervix is filled with a thick mucous secretion known as the cervical plug. This provides a
physical barrier between the vagina and the uterus, in order to protect placental structures and the
developing fetus. In the days prior to calving, the cervical plug is expelled, and the cervical opening
begins to dilate.
The vagina serves as a receptacle for the male’s penis during natural mating. In natural mating, semen is
deposited in the vagina near the cervix. In artificial insemination, a catheter is inserted in the vagina and
manipulated through the cervix, allowing a smaller number of sperm cells to be deposited on the uterine
side of the cervix. Urine is discharged from the urinary bladder through the urethra, which opens into the
base of the vagina. The region behind the urethral opening is called the vestibule and is a common
passageway for both the urinary and reproductive systems. The external opening of the vagina is called
the vulva.
Physiology
The ovary produces the oocyte by a process called oogenesis. In contrast to spermatogenesis in the bull,
which is continuous, oogenesis is cyclic. This cycle of oocyte development in cattle is called the estrous
cycle and is typically 21 days in length. During the estrous cycle, two prominent structures are present
within the ovary: the follicle and corpus luteum.
Each of these structures undergo a development and subsequent regression phase during the estrous cycle.
Follicles begin within the ovary as one of several thousand primary follicles, which consist of a germ cell
surrounded by a layer of flattened cells. This germ cell has the potential to mature into an oocyte if the
follicle completes the development phase. However, only a small percentage of primary follicles continue
through the secondary and tertiary follicular phases and ultimately undergo ovulation. Primary follicles
that never complete development undergo atresia and are replaced by newly formed primary follicles.
The relatively few primary follicles that complete development do so through a series of phases. Many
layers of cells are added to the single layer of cells surrounding the oocyte in the primary follicle and a
central cavity forms. The follicle and cavity within the follicle grow larger, and the oocyte becomes
attached to a stalk of cells on the side of the follicle opposite the future site of ovulation. As the follicle
continues to grow larger, the outer layer of the follicle becomes thinner. This follicle is mature and called
a dominant follicle. The outer layer of the follicle ruptures at the appropriate time, and the oocyte and
contents of the follicular cavity are released. Follicular development occurs in concert with other
reproductive and behavioral functions so that, near the time of ovulation, the female reproductive tract is
prepared to receive both the oocyte from the female and sperm from the male.
Following ovulation, the cells that developed within the follicle undergo a differentiation process. This
process is called luteinization and gives rise to the second prominent ovarian structure, the corpus
luteum (pl. corpora lutea). This structure is often referred to simply as the CL and has the important
function of secreting the hormone progesterone.
The CL goes through a maturation and regression cycle much the same as the follicle. A blood clot-type
structure known as a corpus hemorrhagicum forms in the cavity left by the ruptured follicle and is
transformed into a CL by Day 5 of the cycle (Day 0 = estrus). The CL is fully functional from Day 5 to
Day 15 of the cycle and then begins to regress if the female does not become pregnant. The CL regresses
and no longer secretes progesterone as the follicle of the next estrous cycle begins to develop. As the CL
regresses further, it becomes known as the corpus albicans and remains visible on the ovary for several
subsequent cycles.
Figure 2. The ovarian changes during a typical 21-day estrous cycle in which pregnancy does not
occur. Note that the development and regression of the corpus luteum and of the follicles are
continuous processes.
Figure 2 illustrates the changing structures on the ovary during a typical 21-day estrous cycle. The
dynamic development and regression of the corpus luteum and follicles are a continual process in the
normal cycling cow until she becomes pregnant. In a pregnant female, CL regression does not occur, and
the cyclic activity stops until after calving. A cow generally remains anestrous (does not cycle) for a
period of time following calving. The length of the postpartum anestrous period is on average around 60
days, but this is highly variable among cows based on age, nutrition, lactation, presence of a suckling calf,
environmental stress, and numerous other factors. Management to control the length of this interval is a
main consideration in successful cow-calf enterprises, since a cow must rebreed within 85 days after
calving to produce a calf on a yearly interval.
Any condition that prolongs the period of time that blood levels of progesterone remain high will have the
same effect as pregnancy in stopping the regular 21-day interval between occurrences of estrus.
Occasionally the CL does not regress normally (persistent CL) even though the animal does not become
pregnant. This requires diagnosis and treatment by a veterinarian.
Abnormally short estrous cycles (7 to 11 days) can occur. This condition appears to be caused by either
no corpora lutea being formed, or if one is formed, it is non-functional and progesterone levels remain
low. An estrous cycle can be shortened intentionally by administering a hormone called prostaglandin F2a,
which causes the CL to regress. Prostaglandin F2a is a key tool used in estrus synchronization protocols
Estrus is not always accompanied by ovulation, nor is ovulation always accompanied by estrus. Heat
without ovulation (anovulatory heat) will not result in pregnancy even though the female may be serviced.
Ovulation without behavioral estrus (silent heat) is not uncommon in cows, especially the first few weeks
after calving. Such females will not accept service from a male, but artificial insemination can result in
pregnancy if semen is placed at the appropriate time in advance of ovulation.
There are wide differences between mammalian species in various aspects of the estrous cycle. The cow
is in a group of species that exhibits estrus more than one time per year and is therefore called polyestrus.
Even though cows will cycle at any time during the year, research suggests day length may influence cow
fertility, especially in some breeds or biological types. Slightly lower fertility has resulted during the
short-day length period of the year as compared to the long-day length period of the year.
The hormones of female reproduction
Reproduction in the female is controlled by numerous hormones secreted from specialized glands called
endocrine glands. These secretions are produced in the glandular cells and pass into the blood and lymph
systems for transport to specific parts of the body where they produce their function.
The hormone, estradiol (or estrogen) is produced by the granulosa cells of the follicle. Estradiol has
various effects, including:

Development and function of the secondary sex organs

Receptivity to mating during and other behaviors associated with estrus

Rate and type of growth, especially relative to deposition of fat

Regulation of puberty attainment and length of the postpartum anestrous period
Progesterone, secreted by the corpus luteum, suppresses ovulation of a dominant follicle and the
associated secretion of high levels of estradiol. Therefore, elevated levels of progesterone prevent a cow
from coming into heat. Progesterone is necessary for preparing the uterus to receive the fertilized ovum
and maintains the proper uterine environment for continuation of pregnancy.
Estradiol and progesterone are not separate in their functions since both must be present for certain
processes to occur. For example, the ratio of the concentration of estradiol to progesterone dictates the
onset and duration of behavioral estrus. Development of the uterus is initiated by estradiol and completed
by progesterone. Estradiol causes contraction of the uterus near the time of estrus and ovulation, which
aids in sperm transport. Progesterone has a quieting effect on the uterus so that there are no contractions
which might disturb pregnancy.
The production of ovarian hormones is under direct influence of gonadotropic hormones produced by the
anterior pituitary. Follicle stimulating hormone (FSH) and luteinizing hormone (LH) are secreted from
the pituitary and travel through the blood to the ovary. The release of FSH and LH is mediated
by gonadotropin-releasing hormone (GnRH) by the hypothalamus. FSH stimulates the recruitment,
growth, and development of follicular waves, while LH supports continued development of a dominant
follicle. Additionally, a surge in LH release around the time of onset of estrus causes the follicle to initiate
the ovulatory process and develop into a corpus luteum.
The cyclic rise and decline of the reproductive hormone concentrations is graphically illustrated in Figure
3. This cyclic process continues every 21 days in a normal-cycling cow, but changes if conception occurs.
Following pregnancy and a period of anestrus, the estrous cycle once again continues. Figure 3 shows the
female hormones during a typical estrous cycle.
Figure 3. The rise and decline of reproductive hormones during a typical 21-day estrous cycle.
The estrous cycle
The reproductive cycle of the cow consists of a series of events that occur in a definite order over a period
of days. In the cow, this cycle averages 21 days in length, although this can range from 17 to 24 days. In
this cycle, the reproductive system is prepared for potential establishment and maintenance of pregnancy.
Alternatively, in the event that fertilization does not occur or that establishment or maintenance of
pregnancy fails, the female returns to estrus. Figures 2 and 3 show the ovarian changes and sequence of
events in a typical 21-day cycle in which pregnancy does not occur.

Days 0 to 1
The cow is in for estrus (standing heat) on Day 0 for an average of 18 hours (range 8 to 24 hours).
Shortly after onset of estrus, a surge of LH is released by the pituitary gland. About 30 hours after
the start of the standing heat, the mature dominate follicle ruptures (ovulates).

Days 1 to 2
The cells that formerly lined the follicle change and become the luteal cells of the corpus luteum.
This change in cell forms is caused by hormonal action, primarily that of LH.

Days 2 to 5
The corpus luteum grows rapidly in both size and function. Numerous follicles may be seen on
the ovary at this stage, but by Day 5 they have begun to regress.

Days 5 to 16
The corpus luteum continues to develop and reaches its maximum growth and function about Day
10. It secrets the hormone progesterone, which inhibits (blocks) LH release by the pituitary gland.
During this period, the ovaries are relatively inactive except for the functional corpus luteum and
wave-like follicular development. A dominant follicle will reach maturity but the existence of the
high levels of progesterone inhibit estrus and ovulation.

Days 15-17
The corpus luteum regresses rapidly due to luteolytic activity of the uterus caused by the release
of the hormone, prostaglandin F2a.

Days 18 to 2
The corpus luteum is almost non-functional and this releases the blocking action of progesterone.
Of the several follicles that commence growth, one becomes more prominent by a surge in rapid
growth and activity. As the dominate follicle grows, it secretes increasing amounts of estradiol.
The remainder of the follicles regress.

Day 21 or 0
With the increase in estradiol release by the dominant follicle and a corresponding decrease in
progesterone by the regressing corpus luteum, estrus or heat will occur (cycle has now returned to
Day 0). The high estradiol level in the blood triggers a release of LH near the end of heat.
Following this surge in blood levels of LH, the mature follicle ruptures to release the ovum and
the cellular tissue left behind becomes luteinized in response to the stimulation of a hormonal
complex to form a new corpus luteum (cycle has now returned to Days 1 and 2). Progesterone
again becomes the dominant hormone.
It should be noted that the timing given for the preceding events is only approximate and differs from
female to female based on cycle length and the number of follicular waves per cycle. It should also be
noted that, if fertilization occurs, and the maternal recognition process begins by the release of interferon
tau, the corpus luteum does not regress but continues to function by secreting progesterone for
maintenance of pregnancy.
The Bull’s Reproductive Organs and Its Functions.
Good reproductive performance of a bull (Figure 1) is necessary to obtain a high percent calf
crop when natural service is used for breeding. A bull must be fertile, capable and willing to
mate a large number of cows during a short breeding season for optimum production. A basic
knowledge of the reproductive tract is beneficial for improved management. An understanding of
the bull’s reproductive system will also help the producer better understand breeding soundness
examinations, reproductive problems and breeding impairments.
Anatomy
The reproductive tract of the bull consists of the testicles, secondary sex organs, and three
accessory sex glands. These organs work in concert for formation, maturation and transport of
spermatozoa, which are eventually deposited in the female reproductive tract. The secondary
sex organs are the epididymis, vas deferens and penis. The three accessory sex glands include
the seminal vesicles, prostate and bulbourethral gland (Cowper’s gland). This basic anatomy is
illustrated in Figure 2.
Figure 2. Drawing of the reproductive tract of the bull (from Nebraska Guide G80-536).
Testicle
The testicle is located outside the body cavity in the scrotum and has two vital functions:
producing the spermatozoa, and producing the male hormone, testosterone. Location of the
testicles exterior to the body cavity is essential for normal sperm formation, which occurs only at
4 degrees to 5 degrees below body temperature. The scrotum provides physical protection to
the testicle and helps regulate the temperature for optimum spermatozoa development. This
regulation is done by coordination of three structures: a temperature-sensitive layer of muscle
(tunica dartos) located in the walls of the scrotum, which relaxes when hot and contracts when
cold; the external cremaster muscle within the spermatic cord, which controls the proximity of
the testicle to the body by lengthening or shortening depending on environmental temperature;
and a counter-current temperature exchange regulated by a blood flow process known as the
pampiniform plexus, which is a coil of testicular veins that provide an effective mechanism for
cooling arterial blood entering the testicle and transferring its heat to the venous blood leaving
the testicle.
One or both testicles occasionally fail to descend into the scrotum during embryological
development and are retained in the body cavity. This condition is known as chryptorchidism.
Hormone production by chryptorchid males is near normal and the male develops and behaves
like a normal male, but will generally be subfertile. This condition is genetically inherited,
therefore such males should not be used for breeding.
The testicle contains many long, tiny, coiled tubes known as seminiferous tubules, within which
the sperm are formed and begin to mature. Scattered throughout the loose connective tissue
surrounding the seminiferous tubules are many highly specialized cells, the interstitial cells of
Leydig, that produce testosterone. There are hundreds of individual seminiferous tubules in the
body of the testicle which unite with one another to form a few dozen tubules that exit from the
testicle and pass into the epididymis.
Epididymis
The epididymis is a compact, flat, elongated structure closely attached to one side of the
testicle. It is divided into three regions, the head, body and tail. The many tubules entered the
head of the epididymis from the testicle unite to form a single tubule some 130 to 160 feet in
length. This tubule is convoluted and packed into the 6- to 8-inch epididymis. Four major
functions occur in the epididymis, including the transport of the developing sperm cells from the
testicle to the vas deferens; the concentration of the sperm by absorption of surplus fluids; the
maturation of the developing spermatozoa; and the storage of viable sperm cells in the
epididymis tail. If sexual activity is slowed, resorption of sperm cells from the epididymis tail
occurs.
The epididymis serves as an outlet for all the sperm produced in the testicle and any blockage
of this tube will cause sterility. Temporary blockage due to swelling following an injury or
infection (epididymitis) will result in short-term infertility. If the swelling or infection results in
formation of scar tissue in the tubule, it may permanently block the passage of sperm. If
blockage occurs in both epididymides, the bull will no longer be useful as a breeder. Surgical
removal of the tail of the epididymis (epididectomy) is frequently used as a means of sterilization
for teaser (Gomer) bulls for estrus detection. Epididectomized bulls will still service cows in the
usual manner, but will not deposit sperm in the female reproductive tract.
Vas deferens
The vas deferens, also known as ductus deferens, emerges from the tail of the epididymis as a
straight tubule and passes as part of the spermatic cord through the inguinal ring into the body
cavity. Spermatozoa are transported further along the reproductive tract to the pelvic region
through the vas deferens by contraction of the smooth muscle tissue surrounding this tubule
during ejaculation. Bulls may also be sterilized by a vasectomy in which a section of the vas
deferens is removed so that sperm cannot pass to the outside of the body.
Urethra
The two vas deferens eventually unite into a single tube, the urethra, which is the channel
passing through the penis. The urethra in the male serves as a common passageway for semen
from the reproductive tract and urine from the urinary tract.
Accessory glands
Two of the accessory glands are found in the general region where the vas deferens unite to
become the urethra. Secretions from these glands make up most of the liquid portion of the
semen. In addition, the secretions activate the sperm to become motile. The seminal vesicles
consist of two lobes about 4 to 5 inches long, each connected to the urethra by a duct. The
prostate gland is located at the neck of the urinary bladder where it empties into the urethra.
The prostate is relatively small in the bull, as compared to other species, and does not produce
a very large volume secretion.
The third accessory gland, the Cowper’s glands, are small, firm glands located on either side of
the urethra. The clear secretion that often drips from the penis during sexual excitement prior to
service is largely produced by these glands and serves to flush and cleanse the urethra of any
urine residue that may be harmful to spermatozoa.
One of the accessory glands may occasionally become infected, resulting in semen samples
that are yellow and cloudy and which contain puss cells. It is not uncommon in bulls for the
seminal vesicles to be so affected (seminal vesiculitis). Antibiotic treatment is sometimes
necessary, but time will generally correct the problem.
Penis
The sigmoid flexure is an anatomical structure that provides a means by which the penis is held
inside the sheath except during time of service. Strong retractor muscles hold the penis in the
“S” shaped configuration. Occasionally these muscles are too weak to function properly and a
portion of the penis and sheath lining protrude at all times. This exposes the male to the danger
of injury and this characteristic should be avoided when selecting a herd bull.
Figure 3. Sketches show abnormalities of sperm cells and penis (from Nebraska Guide
G80-536).
The penis is the organ of insemination. Spongy-type material within the penis is filled with blood
during sexual arousal, resulting in erection of the organ. The end of the penis is the glans penis
and is richly supplied nerves, which are stimulated during copulation to induce ejaculation.
Impairments of the glans penis may exist (Figure 3) and should be detected during a fertility
exam.
Regulation of male hormones
The normal functions of male reproduction are largely controlled by hormones that are secreted
from the endocrine glands. The testicle functions as an endocrine gland because of its
production of the male hormone, testosterone, by the intersticial cells. Testosterone has several
major functions:

It is largely responsible for development and maintenance of the male reproductive tract

It causes the development and maintenance of the secondary sex characteristics
associated with masculinity, such as the crest and heavily muscled shoulders of a bull

It is a major factor in the normal sex drive and behavior of the male

It increases muscular and skeletal growth

It is essential for normal sperm formation.
The testicle is, in turn, under the influence of hormones produced by other glands in the body.
The same gonadotropic hormones that regulate ovarian functions in the cow also regulate
testicular functions in the bull. Luteinizing hormone (LH) and follicle stimulating hormone (FSH)
appear to be misnamed as pertaining to male reproduction, yet carry out several important male
functions.
LH and FSH are released from the pituitary gland and cause the testicle to secrete testosterone,
which then acts on the germ cell lining of the seminiferous tubules to stimulate formation of
primordial sperm cells. The maturation of spermatids into fully developed sperm cells requires
the presence of FSH. Normal functioning of the male accessory glands requires testosterone.
Not only is hormone production of the testicle regulated by hormones released by the anterior
pituitary, but the reverse is also true. The level of testosterone in the blood regulates the
secretion of gonadotropic hormones from the anterior pituitary via a feedback system. A proper
balance of all hormones is vital to successful reproductive functions.
Breeding soundness exams
An examination of bulls for breeding soundness before the breeding season can detect the
majority of bulls which have obvious potential fertility problems. This examination should be
performed by an experienced, trained person, usually a veterinarian. It should be pointed out
here that a breeding soundness examination is simply a screening procedure to eliminate bulls
that have a high possibility of being non-fertile. A “fertility test” is a misnomer since techniques
presently available do not allow for accurate prediction of fertility. Results from an actual
breeding season remain the only test of a bull’s breeding ability. For more detailed information
on bull breeding soundness exams, refer to MU Extension publication G2011, Determining
Reproductive Fertility in Herd Bulls. A breeding soundness examination includes an evaluation
of the following components:
Physical examination
The penis should be examined during electro-ejaculation or natural mating, in an erected,
extended state. Figure 2 illustrates possible abnormalities of the penis. Potential problems of the
penis may include hair rings, which restrict circulation, a persistent frenulum or adhesion,
lacerations, growths, scar tissue, deviations, or a urethral fistula. Next the scrotum and testes
should be palpated. The scrotum should be pendulous but well supported. The testes should be
firm and uniform in size and shape. The internal sex organs should be palpated rectally to
ensure proper development and size. Good vision and sound feet and legs should also be
considered when evaluating a bull’s physical abilities to breed.
Scrotal circumference
Scrotal circumference gives an indication of a bull’s ability to produce sperm and is related to
younger age at puberty. Breeds differ somewhat as to scrotal circumference, but 32 centimeters
is generally accepted as the minimum size for yearling bulls to be sound breeds.
Semen evaluation
Four criteria are used to evaluate semen, i.e., volume, concentration, motility and morphology.
Proper training is required to accurately evaluate semen. A scoring system for predicting
potential breeding soundness of bulls as prepared by the Society for Theriogenology, which
incorporates scrotal circumference, semen motility, and semen morphology.
Breeding soundness examinations presently do not include an evaluation of a bull’s sexual drive
or libido. Libido testing is time consuming and requires use of females in estrus and therefore is
difficult to conduct on a large scale. Procedures are being investigated to better evaluate the
willingness and desire of bulls to
mate.